A dielectric porcelain composition has been widely used in electronic devices operating in a high frequency region such as microwave and miliwave. As the characteristics required for the applications, the followings can be cited. That is,
(1) since a wavelength is shortened to 1/∈r1/2 in a dielectric material, the relative dielectric constant ∈r is large to achieve miniaturization,
(2) the dielectric loss in a high frequency region is small, that is, the Qf value is high, and
(3) the temperature coefficient τf of a resonant frequency is small and stable.
Furthermore, it is important as well that the temperature coefficient τf is controllable in a predetermined range.
So far, as such a dielectric porcelain composition for use in high frequency, for instance, a La—Ti—Al—O-based one (see non-patent literature 1) has been known. However, the characteristics thereof are: ∈r=36, Qf value=45,000 GHz and τf=−2 ppm/° C., that is the Qf value is low.
Furthermore, in a Ba(Zn1/3Nb2/3)O3-based one (see non-patent literature 2), the characteristics such as ∈r=41, Qf value=86,000 GHz and τf=+31 ppm/° C. are obtained. However, a dielectric porcelain composition having small τf has not been obtained yet.
Recently, as a material that has a high dielectric constant and a high Qf value, La—Al—Ca—Ti-based-oxide dielectric porcelain (see patent literature 1) and La—Al—Sr—Ti-based-oxide dielectric porcelain (see patent literature 2) have been proposed. These materials have excellent characteristics such as the relative dielectric constant ∈r in the range of from 30 to 48 and the Qf value in the range of from 20,000 to 75,000 (values at 1 GHz). However, a dielectric porcelain composition having small τf has not been obtained yet.
Furthermore, in La—Al—Ca—Sr—Ba—Ti-based oxide dielectric porcelain, it has been proposed that α-Al2O3 is contained as a crystal phase to thereby increase the Qf value (see patent literature 3). Although this material has such excellent characteristics as 30,000 or more in the Qf value, the value of τf is relatively large in plus or minus.
In these materials, although the relative dielectric constant ∈r and the Qf value can be increased, characteristics of τf are not sufficient and there is no idea of controlling τf.
The applicant has previously proposed a dielectric porcelain composition for use in microwave, which has the dielectric characteristics such as ∈r=35 to 45, Qf value=50,000 Ghz or more and τf=0±10 ppm/° C. (see patent literature 4). In this composition, when, in La—Al—Sr—Ti-based oxide, a particular amount of Ga is added, the Qf value can be increased, and when a particular amount of Pr is further added, the τf value can be controlled to 0±10 ppm/° C.    Non-patent literature 1: Japanese Journal of Applied Physics, Vol. 36 (1997) 6814    Non-patent literature 2: Erekutoroniku Seramikusu (Electronic Ceramics), September (1993), pages 4-10    Patent literature 1: Japanese Patent No. 2,625,074    Patent literature 2: JP-A-11-130528    Patent literature 3: JP-A-11-106255    Patent literature 4: WO 02/36519 A1